Tri-orthogonal antenna system with variable effective axis



NOV. 21, 1967 E, l, SCHWARTZ ET AL 3,354,459

TRI-ORTHOGONAL ANTENNA SYSTEM WITH VARIABLE EFFECTIVE AXIS Filed Aug. 5, 1965 5 Sheets-Sheet 1 & v 23 32 VAR/ABLE VA R/A 51E AMPl/F/ERS INVENTORfi FIG 5 5%??? 53X??? 2 Nov. 21, 1967 E. I. SCHWARTZ ET AL 3,354,459

TRI-ORTHOGONAL ANTENNA SYSTEM WITH VARIABLE EFFECTIVE AXIS 5 Sheets-Sheet Filed Aug. 5, 1965 Nov. 21, 1967 E. SCHWARTZ ET AL 3,354,459

TRI-ORTHOGONAL ANTENNA SYSTEM WITH VARIABLE EFFECTIVE AXIS 5 Sheets-Sheet Filed Aug. 5, 1965 United States Patent 3,354,459 TRI-ORTHOGONAL ANTENNA SYSTEM WITH VARIABLE EFFECTIVE AXIS Edmund H. Schwartz, Fairlawn, N1, and James Chin- Bow, New York, N.Y., assiguors to Devenco Incorporated, New York, N.Y., a corporation of New York Filed Aug. 5, 1965, Ser. No. 477,573 11 Claims. (Cl. 343100) ABSTRACT OF THE DESCLOURE Antenna system including three antennas having mutually perpendicular axes and a common point of intersection, i.e., common phase center. Individual circuit connected to each antenna, each circuit including means for independently varying intensity of signal carried by circuit, and/ or means for independently varying the time phase of signal carried by circuit.

Each circuit may have means for measuring the intensity and/ or the time phase of the signal received by its respective antenna.

This invention relates to transmitting and receiving signals in the form of electromagnetic waves, and more particularly to an antenna system for this purpose. Coordinately, the invention relates to an antenna especially adapted for use in the present system.

It is well known that if the polarization of an electromagnetic wave to be received is known in advance, a receiving antenna can be adjusted to receive the signal with maximum efliciency. More specifically, if the plane of polarization of the vector representing the wave is known in advance, the dipole of a receiving antenna can be positioned parallel to the vector and the signal will be received with maximum efficiency. Alternatively, if it is desired to null the signal, i.e. not receive it at all, the dipole of the antenna is positioned perpendicular to the signal vector. Thus, in theory, if the polarization of the signal sent by a transmitter is known, and there is no interference between the transmitting station and the receiving station, it is a simple matter to position the receiving antenna to either receive the signal with maximum efficiency, or to null the signal.

In most practical cases, however, it is almost impossible to predict what the polarization of a signal will be when it reaches the receiving antenna even if its polarization at the time it leaves the transmitter is known. The reason is that there are usually obstacles, e.g. buildings, antennas, and airplanes, present between the transmitting and receiving stations which interfere with and alter the characteristics of the transmitted-wave. Consequently, by the time the signal reaches the receiving antenna, it may have any conceivable polarization entirely unrelated to its polarization when originally transmitted. For this reason, it has been virtually impossible to determine in advance what configuration and orientation an antenna should have to receive a particular transmitted signal with maximum efficiency, or to null the signal. The problem becomes even more difficult when the transmitting and receiving stations are in relative motion.

It is a general object of the present invention to provide an antenna system which is capable, without the employment of moving parts, of receiving any signal with maximum efliciency or of nulling any signal.

It is another object of the invention to provide such an antenna system capable of accomplishing these results without requiring any knowledge of the location of obstacles which interfere with the transmitted signal, or refraction, difiiraction, and reflection efl ects, or the polarization changes undergone by the signal.

It is a further object of the invention to provide a tool for determining the plane of polarization of any received signal vector, and the rotational polarization, if any, of the signal vector.

As used in the following description, and the appended claims, the term plane of polarization refers to the orientation, in three dimensional space, of the signal vector, i.e. the plane containing the electromagnetic signal wave, incident upon the antenna, or leaving the antenna. The term rotational polarization refers to the locus traced by the signal vector as it rotates about the phase center of the antenna; this locus may be circular or elliptical depending upon whether or not the amplitude of the vector varies as it rotates.

It is still another object of the invention to provide an antenna structure admirably adapted for use as part of the antenna system of the invention.

To achieve the objectives set forth above, the invention provides an antenna system including three antennas having mutually perpendicular axes and a common point of intersection. An individual circuit is connected to each antenna for carrying a signal to its antenna, if the antenna is being used to transmit, or for carrying a signal from the antenna to a receiving apparatus, if the antenna is being used to receive a signal. In each circuit is a means for independently varying the intensity of the signal carried by the circuit, and/or a means for independently varying the time phase of the signal carried by the circuit. If the antenna is thought of as being part of a transmitter arrangement, it will be appreciated that by appropriately adjusting the three intensity-varying means, a signal having any desired angle of polarization can be produced. Similarly, by appropriately adjusting the three timephase-varying means, a signal having any desired rotational polarization can be produced.

The antenna structure of the invention includes three dipoles, the axes of the dipoles being mutually perpendicular and intersecting at a common point. Preferably, the dipoles are so mounted on a common hub that they may be collapsed into a compact condition for transportation and storage.

Other objects and advantages of the invention will be apparent from the following description in which referonce is made to the accompanying drawings.

In the drawings:

FIG. 1 is a schematic diagram of an antenna system according to this invention including means for varying the intensity of the signal carried to or from each antenna;

FIG. 2 is a diagram similar to FIG. 1 in which timephase-varying means are shown in place of the intensityvarying means;

FIG. 3 is a diagram similar to FIG. 1 showing both an intensity-varying means and a time-phase-varying means in each antenna circuit;

FIG. 4 is a diagram similar to FIG. 3 including means for measuring the intensity and time phase of the signal in each antenna circuit;

FIG. 5 is an explanatory view showing an arbitrary signal vector in relation to a three-dimensional coordinate system;

FIG. 6 is a fragmentary perspective view of an antenna arrangement especially adapted for use in the present antenna system;

FIG. 7 is a view of the antenna looking along the length of one of its dipoles;

FIG. 8 is a view of the antenna looking along the length of another of its dipoles;

FIG. 9 is a top plan view of FIG. 6;

FIG. 10 is a cross-sectional view taken along line Iii-10 of FIG. 9;

J FIG. 11 is a cross-sectional view taken along line 1111 of FIG. 10; and

FIG. 12 is a view similar to FIG. 10 showing the antenna dipoles in collapsed condition.

It is well known that when an electromagnetic wave is transmitted by an antenna, the plane of polarization of the vector representing the wave, in the absence of interference, is such that the vector is parallel to the axis of the antenna. Furthermore, a transmitted signal carried by a wave will be received with maximum er"- ficiency when the axis of the receiving antenna is parallel to the signal vector, and the signal will be nulled when the axis of the receiving antenna is perpendicular to the signal vector.

In the antenna system of the present invention, the efiective axis of the antenna arrangement is adjustable, the adjustment being made electronically rather than physically. Thus, without actually moving the antenna structure, the eifective axis of the antenna can be altered so that it assumes any desired orientation.

To facilitate an understanding of the present antenna system, reference will be made first to FIG. in which three dimensional space is represented by three mutually perpendicular axes X, Y, and Z, intersecting at a common point 11. A signal vector 10, arranged at an acute angle to each of the axes X, Y, and Z, is intended to be representative of any arbitrary signal vector. Such a vector has a projection on each axis, the arrow 12 representing the projection on the X axis, and the arrows 13 and 14 representing the projections on the Y and Z axes, respectively. Thus, it will be appreciated that any arbitrary signal vector can be broken into three signal projections, the axes of which are mutually perpendicular. Conversely, any arbitrary signal vector can be created by combining three appropriate signals having mutually perpendicular axes of polarization. The relationship between the lengths of the arrows 12, 13 and 14 depends upon the plane of polarization of the vector 10. Obviously, if a signal vector is perpendicular to any axis, the length of the projection along that axis will be zero (which is another way of saying that a signal can be nulled by positioning an antenna dipole perpendicular to the signal vector), and if the vector is parallel to any axis, the length of the projection along that axis will be equal to the length of the vector (which is another way of saying that a signal is received with maximum efficiency when an antenna dipole is positioned parallel to the signal vector). In all other cases, the length of the projection on any axis is some value between zero and the length of the vector.

The manner in which these principles are employed by the present invention will now be described with reference to FIG. 1. Three antennas, 15, 16, and 17 shown schematically in FIG. 1, represent three antennas having mutually perpendicular axes which intersect at a common point and have a common phase center. In the case of dipoles, the phase center is the physical center of the dipole, and the point at which the cable is connected to the antenna. Thus, the axes of the three antennas are arranged identical to the arrangement of the axes X, Y, and Z of FIG. 5. A separate circuit 18 extends between each antenna and a means 19, which in turn is connected to a terminal 20. The means 19 may be a device for summing all the signals in the circuits 18, when the antenna system is being used as part of a receiving arrangement, and delivering the combined signals to receiving equipment (not shown) connected to the terminal 20. Alternatively, when the system is being used as part of a transmitter arrangement, the means 19 may be a device for dividing a signal, reaching it from transmitter equipment (not shown) connected to terminal 20, between the three circuits 18.

Each of the circuits 18 is provided with an independently operable, variable amplification means. These three devices, 21, 22, and 23, may be variable amplifiers or attenuators, and permit independent adjustment of the intensity or amplitude of the signal in each of the circuits. Since the lengths of the arrows 12, 13, and 14 in FIG. 5 are directly related to the intensity or amplitude of the signals they represent, it is obvious that the plane of polarization of the resultant vector 10 can be changed by varying the intensities of the signals whose axes of polarization coincide with the X, Y, and Z axes. In other words, the effective axis of the composite antenna 15, 16, and 17, can be adjusted to assume any angle in three dimensional space simply by appropriately adjusting the three amplifiers 21, 22, and 23. Actually, only two of these amplifiers need necessarily be adjusted in order to yield an etfective axis having any desired orientation, since it is the relationship between the intensity of the signals in the three circuits, and not their absolute value, which determines the angle of the resultant vector.

Assume that the axis of the antenna 15 of FIG. 1 corresponds to the X axis of FIG. 5, and the axes of the antennas 16 and 17 correspond to the axes Y and Z, respectively. In such a case, the length of the arrow 12 is adjustable by means of the amplifier 21, and the lengths of the arrows 13 and 14 are adjustable by means of the amplifiers 22 and 23, respectively. Now, if the antenna system of FIG. 1 is being used as part of a receiving arrangement, and it is desired to receive a signal represented by the vector 10, the amplifiers 21, 22, and 23 are adjusted so that their gains have the same relationship to each other as do the projections 12, 13 and 14. Consequently, the effective axis of the antenna 15, 16, and 17 is parallel to the vector 10, and the signal is received with maximum efficiency.

Proper adjustment of the amplifiers can be accomplished by a trial and error technique. The amplifiers are first adjusted so that they all have the same sense, say a positive sense. The sense of each amplifier is then, in turn, reversed, i.e., the phase of its output is changed by If, after any particular reversal, reception of the signal is enhanced, the new sense of that particular amplifier is retained. If, on the other hand, reversal causes detraction in signal reception, the amplifier is returned to its original sense. Once the proper sense of each amplifier is determined, the gain of each amplifier is adjusted, in turn, until the signal is received with maximum signal-to-noise ratio. Adjustment of the amplifiers 21, 22, and 23, for reception of a signal with maximum efficiency is then complete.

Should it be desired to null a particular signal, it is necessary to shift the effective axis of the antenna into a plane perpendicular to the vector representing the signal. An example of this procedure is illustrated in FIG. 5. The signal vector 10 has a projection on the Y-Z plane represented by the dot-dash arrow 26. Assume at the outset that the effective axis of the antenna is colinear with the vector 10, and it is now desired to null the signal. First, the sense of the amplifier 22, which controls the length and direction of the arrow 13, is reversed in order to swing the projection 26 of the effective antenna axis to the opposite side of the Z axis. Then, either amplifier 22 or 23 is adjusted to cause the projection on the Y-Z plane to assume a position perpendicular to the projection 26, as indicated by the dot-dash arrow 27. If the projection 26 happens to be at a 45 angle to the Z axis, no adjustment of the amplifier 22 or 23 will be required since upon reversal of the sense of amplifier 22 the projection 27 will at once be perpendicular to the projection 26. The new effective axis of the antenna is illustrated by the dotted arrow 28. Since this axis is perpendicular to the vector 10, the antenna will be blind to, i.e., will not pick up, the signal represented by the vector 10.

It should be noted that in the example given above, no particular adjustment of the amplifier 21, which controls the length and direction of arrow 12, is required 5 to null the signal 10. Varying the gain and/or sense of the amplifier 21 will serve merely to rotate the axis 28 in a plane perpendicular to the vector 10. Thus, there are an infinite number of positions of the effective axis of the antenna which will null the signal 10, and therefore it is possible to receive a different signal, even a signal transmitted at the same frequency as the signal 10, while nulling the signal 10.

The antenna system has been described above in connection with a receiving arrangement. However, it may also be employed as part of a transmitting installation. In such a case, if it is desired to transmit a signal having a particular plane of polarization, the amplifiers 21, 22, and 23 are adjusted to cause the effective axis of the antenna to be parallel to the desired angle of polarization of the signal to be transmitted.

The discussion thus far has dealt with transmitting and receiving signals having particular angles of polarization. The present antenna system is also useful for transmitting and receiving rotationally polarized waves. A rotationally polarized wave is one whose axis of polarization rotates, i.e., whose plane of polarization changes with time. Consider a two coordinate system such as that represented by the X and Y axes of FIG. 5. At an instant of time when a vector representing a rotationally polarized wave is parallel to the X axis, the projection of the vector upon the X axis will be a maximum and equal to the length of the vector. The projection upon the Y axis, however, will be zero. As the vector rotates, the projection on the X axis will diminish and the projection on the Y axis will increase. After the vector has rotated through 90, the projection on the X axis will be zero and on the Y axis will be a maximum. The effect on the X and Y projections of continued rotation of the vector through the remaining 270 of its orbit will be obvious.

As was brought out above, a resultant vector can be produced by combining two or more signals analogous to the projections just described. Thus, a vector rotationally polarized in the XY plane, can be produced by transmitting a sinusoidal wave having an axis of polarization parallel to the X axis, and a second sinusoidal wave, 90 out of time phase with the first, having an axis of polarization parallel to the Y axis. The resultant of these two waves will be a constantly rotating vector. Addition of a third wave, in phase with one of the other two waves, and having an axis of polarization parallel to the Z axis will not affect the rotation of the resultant vector except to change its orientation by moving it out of the X-Y plane.

An antenna system, according to this invention, for transmitting or receiving rotationally polarized waves is shown in FIG. 2. The antennas 15, 16, and 17, and the elements 19 and 20 are identical to the corresponding elements shown in FIG. 1. A separate circuit 29 connects each of the antennas 15, 16, and 17 to the device 19, and an independently operable phase shifter is located in each circuit. The phase shifter 30 controls the time phase of the signal being carried to or from the antenna 15, and the phase shifters 31 and 32 serve a comparable function with respect to the antennas 16 and 17, respectively. If the system of FIG. 2 is being used to transmit a wave, adjusting any one of the phase shifters so that its respective signal is 90 out of time phase with the signals controlled by the other two phase shifters will, for the reason pointed out above, produce a rotationally polarized wave.

A rotationally polarized wave will be produced as long as any two of the phase shifters are adjusted so that their respective signals are 90 out of phase. The third phase shifter can be adjusted so that its respective signal is in phase with either one of the other two signals, or is 90 out of phase with one and 180 out of phase with the other. The efiect of changing the phase relationship of the third signal with respect to the other tWo will be to change the plane in which the signal vector rotates. For example, if the phase shifters 30 and 31 are adjusted so that the signals they control are 90 out of phase, the

amplitude of the signal transmitted by antenna 15 (the axis of which extends along the X axis in FIG. 5) will be a maximum when the amplitude of the signal transmitted by antenna 16 (the axis of which extends along the Y axis in FIG. 5) is zero, and vice versa. If the phase shifter 32 is adjusted so that the signal transmitted by the antenna 17 (the axis of which extends along the Z axis in FIG. 5) is in phase with the signal of antenna 15, the resultant vector will rotate in a plane containing the Y axis and at 45 angles to both the X and Z axes. If the phase shifter 32 is readjusted so that the signal of antenna 17 is in phase with the signal of antenna 16, the resultant vector will rotate in a plane containing the X axis and at 45 angles to both the Y and Z axes.

Since no intensity-varying means, comparable to the amplifiers 21, 22, and 23 of FIG. 1, are included in the arrangement of FIG. 2, the signals transmitted by all three antennas will have the same maximum amplitude. Therefore, the resultant signal will have a circular polarization, i.e., the length of the rotating vector representing the signal will remain the same at all times. In order to produce an elliptically polarized signal, an arrangement such as that shown in FIG. 3 may be used. This arrangement is, in effect, a combination of the arrangements of FIGS. 1 and 2. Separate circuits 33 connect each of the antennas 15, 16, and 17 to the device 19. The signal carried to the antenna 15, for transmission, is controlled by the amplifier 21 and phase shifter 30; the signal carried to antenna 16 is controlled by the amplifier 22 and phase shifter 31; and the signal carried to antenna 17 is controlled by the amplifier 23 and phase shifter 32.

' Assume that the phase shifters 30 and 31 are adjusted so that the signals they control are out of phase, and ignore the phase shifter 32 for the moment. If the gain of amplifier 22 is adjusted to be twice the gain of amplifier 21, the maximum amplitude of the signal transmitted by antenna 15 will be equal to half the maximum amplitnde of the signal transmitted by antenna 16. Consequently, the resultant vector will be twice as long, at the instant it is parallel to the Y axis (FIG. 5), as it was at the instant it was parallel to the X axis. Thus, the signal is elliptically polarized. If the phase shifter 32 is now adjusted to any of its several possible settings, variation of the gain of amplifier 23 will serve to alter the plane in which the resultant vector rotates. It will be appreciated, therefore, that the arrangement of FIG. 3 can be employed to transmit a wave having any possible rotational polarization. Furthermore, if the phase shifters 30, 31, and 32 are adjusted so that the signals carried by the three circuits 33 are in phase, a nonrotationally polarized wave having any possible plane of polarization can be produced.

The arrangements of either of FIGS. 2 and 3 can, of course, be used as part of a receiving installation as well as part of a transmitting installation. In such a case, instead of a rotationally polarized wave being transmitted, the effective axis of the antenna will be rotationally polarized. Thus, with the arrangement of FIG. 3, the effective axis of the antenna can be given any desired circular or elliptical polarization. Hence, the effective axis of the antenna can at all times be maintained parallel to the vector representing a wave having any possible polarization, and thus any Wave can be received by the present antenna system with maximum efficiency. Furthermore, since the direction of rotation of the effective axis of the antenna can be reversed by adjusting any one of the phase shifters so as to shift the phase of its respective signal by any possible signal can be nulled. This is because, as is well known, an antenna whose effective axis rotates in one direction, e.g. right-hand polarized, is blind to a signal represented by a vector which rotates in the opposite direction, e.g. left-hand polarized.

In certain circumstances, it is necessary to receive a signal transmitted by a remote source, and then transmit another signal back to the source. At present, this is often accomplished by means of an array of antennas, sometimes referred to as a retrodirective array. The array usually comprises a large number of antennas positioned in a particular spaced-apart relationship. A wavefront from a remote source usually strikes the antennas of the array at different times, due to the spacing between the antennas, and therefore, the phase of the wave is different as it strikes each antenna. By using this phase information, signals can be transmitted by the antennas of the array which are out of phase with one another but which produce a resultant signal directed toward the remote source.

According to this invention, as illustrated in FIG. 4, a retrodirective effect can be produced by means of just three antennas 15, 16, and 17, having mutually perpendicular axes which meet at a common point. Separate circuits 34, 35 and 36 connect the antennas, respectively, to a device 19. This device can combine the signals carried by the three circuits when the system is receiving a signal from a remote source, and deliver the sum to a terminal 20. Alternatively, the device can divide a signal received from terminal between the three circuits 34, 35, and 36 when the system is transmitting a signal back to the remote source. Means for measuring the intensity or amplitude of the signal carried by each circuit is present in the circuit. For example, voltmeters 37, 38, and 39 are arranged in the circuits 34, 35, and 36, respectively. Each voltmeter is located between its respective antenna and amplifier. More specifically, the voltmeter 37 is located between the antenna 15 and the amplifier 21.

In addition, means for determining the phase relationship between the signals carried by the three circuits is provided. Thus, for example, a phase detector 40, is connected between the circuits 34 and 35, a phase detector 41 is connected between the circuits and 36, and a phase detector 42 is connected between the circuits 34 and 36. The phase detector connections in each circuit are made between their respective antenna and phase shifter. Specifically, the phase detector is connected to the circuit 34 at a point between the antenna 15 and phase shifter 30.

When a wave from a remote source, having any arbitrary polarization, impinges upon the antennas 15, 16 and 17, the projection of the wave on each of the antennas will cause a signal to be carried by each of the circuits. The amplitude of each signal corresponds to the length of the projection on its respective antenna. Thus, the amplitudes measured by voltmeters 37, 38, and 39 correspond to the lengths of the projections on the antennas 15, 16, and 17, respectively. Furthermore, if the impinging wave is rotationally polarized, the amplitudes of the signals in the three circuits will vary with a particular relationship, and this phase relationship between the signals will be detected by the phaes detectors 40, 41, and 42.

Now, in order to transmit a signal back to the remote source, the gains of the amplifiers 21, 22, and 23 are adjusted so that they have the same relationship to each other as the relationship between the amplitudes of the signals measured by their respective voltmeters 37, 38, and 39. For example, if the amplitude measured by voltmeter '37 is twice the amplitude measured by voltmeter 38, amplifier 21 will be adjusted so that its gain is twice that of amplifier 22. In addition, phase shifters 30, 31, and 32 are adjusted so that any signals controlled by them will have the same phase relationship as the phase relationship between the signals measured by the phase detectors 40, 41, and 42. For example, if the phase detector 40 indicates that the signal in circuit 35 is leading the signal in circuit 34 by 90, the phase shifters 30 and 31 will be adjusted so that any signal controlled by phase shifter 31 will lead a signal controlled by phase shifter 30 by 90.

When the amplifiers and phase shifters have been adjusted, as described above, a signal to be transmitted is conducted to the device 19 from terminal 20. and is divided between the three circuits 34, 35, and 36. The

signals which reach the antennas 15, 16, and 17 will, at any instant, have the same amplitude and phase relationship as the relationship between the projections on the antennas of the signal received from the remote source, due to the settings of the amplifiers and phase shifters. Consequently, the resultant signal transmitted by the antennas 15, 16, and 17 will have exactly the same polarization as the signal received from the remote source. In cases where there is relative movement between the remote source and the present antenna system, or where moving objects interfere with the waves traveling between the rornote source and the present antenna system, automatic means of well known kind can be employed to alter the adjustments of the amplifiers and phase detectors in response to variations in the values measured by the voltmeters and phase detectors, respectively. Thus, the polarization of the wave transmitted by the antennas 15, 16, and 17 is maintained the same as the polarization of the wave received from the remote source even though there may be moment-to-moment changes in the polarization of the received wave.

From the above description, it will be appreciated that the present invention provides an antenna system capable (a) receiving any signal with maximum efficiency regardless of its plane of polarization or its rotational polarization;

(b) transmitting a signal having any conceivable polarization;

(c) nulling any signal;

(d) nulling any signal while at the same time receiving with maximum efficiency a signal having a different polarization; and

(e) transmitting a signal directly to a remote source after receiving a signal from the source, without necessarily knowing the location of the source or the nature of any interference between the remote source and the antenna installation.

In addition to the capabilities set forth above, the antenna system of this invention represents a useful tool for analyzing a received signal. The three projections of the signal can be tabulated for various points in a given space, and the tabulations repeated at different frequencies. This will yield valuable information, unknown until now, about the effects of geography on receiving such signals, particularly broad spectrum signals.

An arrangement of three antennas, adapted for use in the present system is shown in FIGS. 6-12. The arrangement includes a generally cylindrical hub having a longitudinal bore 46 adapted to receive a supporting pole 47. Extending from the hub are three antennas or dipoles 48, 49, and 50, the axes of which are mutually perpendicular and meet at a common point within the confines of the hub. This relationship can be seen in FIGS. 7 and 8. FIG. 7 shows the perpendicularity between dipoles 48 and 49, and FIG, 8 shows the perpendicularity between dipoles 49 and 50.

Each dipole comprises two identical U-shaped members. both arms of each member being arranged in a plane containing the longitudinal axis of the hub. Thus, if the pole is thought of as being vertical, both arms of each U-shaped member are arranged in the same vertical plane. Since all the dipoles are identical to one another, for the sake of convenience only one, the dipole 48, will be described in detail. The dipole 48 includes U-shaped members 51 and 52, the member 51 having an upper arm and a lower arm 56, and the member 52 having an upper arm 57 and a lower arm 58. The members 51 and 52 extend in opposite directions from the hub 45 at an angle of about 45 to the longitudinal axis of the hub.

The free ends of the arms of the U-shaped members 51 and 52 are secured to the hub by suitable fasteners. Thus, the free ends of the upper arms 55 and 57 (see FIGS. 6, 9, and 10) are mounted on the hub 45 by means of screws 59. The free end of each of the lower arms 56 and 58 (see FIGS. 6, 10, and 11) is fastened, by means of a screw 60, to an insulating block 61 mounted on the hub 45. The axes of the screws 60 are perpendicular t the longitudinal axis of the hub, i.e. in the present example the axes of the screws 60 are horizontal. Each of the members 51 and 52 can be pivoted about its respective screw 60 when the screw 59 is removed. Consequently, for purposes of storage and shipment, each U-shaped member can be swung, in a vertical plane, into a position wherein its axis is paralled to the longitudinal axis of the hub 45 and to the pole 47, as shown in FIG. 12. When it is desired to use the antenna, the U-shaped members are simply pivoted back to the positions shown in FIG. and the screws 59 replaced in order to maintain the members 51 and 52 in their operative positions.

Adjacent to each of the insulating blocks 61 the hub 45 is provided with a hole 62 for accommodating an electrical conductor (not shown). Each conductor is connected to the free end of one of the lower arms 56 or 58 by means of the screw 60, and the conductor extends through the hole 62, the bore 46, and the interior of the hollow pole 47 to suitable circuitry, such as one of the circuits 33 of FIG. 3.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claims.

What is claimed is:

1. An antenna system comprising three antennas having mutually perpendicular axes and a common phase center at a common point of intersection, a circuit connected to each antenna for carrying a signal to or from said antenna, and means in each circuit for independently varying the intensity of its respective signal, whereby said system can be adjusted so that its effective axis has any possible 3 dimensional spatial orientation.

2. An antenna system comprising three antennas having mutually perpendicular axes and a common phase center at a common point of intersection, a circuit connected to each antenna for carrying a signal to or from said antenna, and means in each circuit for independently varying the time phase of its respective signal, whereby said system can be adjusted so that if it were part of a transmitter arrangement it could transmit a signal having a rotational polarization.

3. An antenna system comprising three antennas having mutually perpendicular axes and a common phase center at a common point of intersection, a circuit connected to each antenna for carrying a signal to or from said antenna, means in each circuit for independently varying the intensity of its respective signal, and means in each circuit for independently varying the time phase of its respective signal, whereby said system can be adjusted so that if it were part of a transmitter arrangement it could transmit a signal having any possible rotational polarization.

4. An antenna system as defined in claim 3 including means for summing the signals in all of said circuits, and a receiver arranged to receive the sum of said signals.

5. An antenna system intended to receive a signal from a source and then transmit a signal having the same polarization as the received signal, comprising (a) three antennas having mutually perpendicular axes and a common point of intersection,

(b) means for measuring the intensity of the signal received by each antenna,

(c) a circuit connected to each antenna for carrying a signal, to be transmitted, to its respective antenna, and

(d) means in each circuit for varying the intensity of the signal carried by the circuit,

whereby the intensity of the signal carried by each cirlb cuit can be made proportional to the intensity of the signal received by its respective antenna so that the spatial orientation of the vector representing the transmitted signal will be the same as the spatial orientation of the vector representing the received signal.

6. An antenna system intended to receive a signal from a source and then transmit a signal having the same polarization as the received signal, comprising (a) three antennas having mutually perpendicular axes and a common point of intersection,

(b) means for measuring the time phase of the signal received by each antenna,

(c) a circuit connected to each antenna for carrying a signal, to be transmitted, to its respective antenna, and

(d) means in each circuit for varying the time phase of the signal carried by the circuit,

whereby the time phase of the signal carried by each circuit can be made to have the same relationship to the time phases of the signals carried by the other circuits as the time phase of the signal received by its respective antenna is related to the time phases of the signals received by the other antennas so that the rotational polarization of the transmitted signal will be the same as the corresponding polarization of the received signal.

7. An antenna system intended to receive a signal from a source and then transmit a signal having the same polarization as the received signal, comprising (a) three antennas having mutually perpendicular axes and a common point of intersection,

(b) means for measuring the intensity of the signal received by each antenna,

(0) means for measuring the time phase of the signal received by each antenna,

(d) a circuit connected to each antenna for carrying a signal, to be transmitted, to its respective antenna, (e) means in each circuit ((1) for varying the intensity of the ignal carried by the circuit, and

(1?) means in each circuit (d) for varying the time phase of the signal carried by the circuit,

whereby the intensity of the signal carried by each circuit can be made proportional to the intensity of the signal received by its respective antenna so that the spatial orientation of the vector representing the transmitted signal will be the same as the spatial orientation of the vector representing the received signal, and the time phase of the signal carried by each circuit can be made to have the same relationship to the time phases of the signals carried by the other circuits as the time phase of the signal received by its respective antenna is related to the time phases of the signals received by the other antennas so that the polarization of the transmitted signal Will be the same as the corresponding polarization of the received signal.

8. An antenna arrangement comprising a hub, and three dipoles projecting from said hub, each of said dipoles being perpendicular to the other two, and the axes of all of said dipoles intersecting at a common point, said point being the phase center of each dipole.

9. An antenna arrangement as defined in claim 8 including a pole for supporting said hub, said pole being arranged at the same acute angle to all of said dipoles.

10. An antenna arrangement as defined in claim 8 wherein each of said dipoles includes a pair of U-shaped members, the corresponding arms of each pair of U- shaped members extending along the same line but in opposite directions from said hub, and both arms of each U-shaped member being arranged in a plane containing said pole.

11. A method of nulling one signal while receiving another signal with the same antenna system, comprising the steps of providing an antenna system including three References Cited UNITED STATES PATENTS 2,532,428 12/1950 Smith 343-100.3 3,103,663 9/1963 Parker 343-l13 X 3,133,283 5/1964 Ghose 343100.3

12 8/1964 Newman 343--100.3 12/1947 Brown 343854 X 3/1 53 Root 343-854 X lZ/l953 Mural 343-854 X 3/1956 Hernphill 343854 X FOREIGN PATENTS 2/1960 Great Britain. 2/1955 Italy.

RICHARD A. FARLEY, Primary Examiner.

CHESTER L. JUSTUS, RODNEY D. BENNETT,

Examiners.

H. C. WAMSLEY, Assistant Examiner. 

5. AN ANTENNA SYSTEM INTENDED TO RECEIVE A SIGNAL FROM A SOURCE AND THEN TRANSMIT A SIGNAL HAVING THE SAME POLARIZATION AS THE RECEIVED SIGNAL, COMPRISING (A) THREE ANTENNAS HAVING MUTUALLY PERPENDICULAR AXES AND A COMMON POINT OF INTERSECTION, (B) MEANS FOR MEASURING THE INTENSITY OF THE SIGNAL RECEIVED BY EACH ANTENNA, (C) A CIRCUIT CONNECTED TO EACH ANTENNA FOR CARRYING A SIGNAL, TO BE TRANSMITTED, TO ITS RESPECTIVE ANTENNA, AND (D) MEANS IN EACH CIRCUIT FOR VARYING THE INTENSITY OF THE SIGNAL CARRIED BY THE CIRCUIT, WHEREBY THE INTENSITY OF THE SIGNAL CARRIED BY EACH CIRCUIT CAN BE MADE PROPORTIONAL TO THE INTENSITY OF THE SIGNAL RECEIVED BY ITS RESPECTIVE ANTENNA SO THAT THE SPATIAL ORIENTATION OF THE VECTOR REPRESENTING THE TRANSMITTED SIGNAL WILL BE THE SAME AS THE SPATIAL ORIENTATION OF THE VECTOR REPRESENTING THE RECEIVED SIGNAL. 